come in at the commencement of the tertiary series.
And now one of the richest known accumulations of fossil mammals belongs
to the middle of the secondary series; and true mammals have been
discovered in the new red sandstone at nearly the commencement of
this great series. Cuvier used to urge that no monkey occurred in any
tertiary stratum; but now extinct species have been discovered in India,
South America and in Europe, as far back as the miocene stage. Had it
not been for the rare accident of the preservation of footsteps in
the new red sandstone of the United States, who would have ventured to
suppose that no less than at least thirty different bird-like animals,
some of gigantic size, existed during that period? Not a fragment of
bone has been discovered in these beds. Not long ago, palaeontologists
maintained that the whole class of birds came suddenly into existence
during the eocene period; but now we know, on the authority of Professor
Owen, that a bird certainly lived during the deposition of the upper
greensand; and still more recently, that strange bird, the Archeopteryx,
with a long lizard-like tail, bearing a pair of feathers on each joint,
and with its wings furnished with two free claws, has been discovered in
the oolitic slates of Solenhofen. Hardly any recent discovery shows more
forcibly than this how little we as yet know of the former inhabitants
of the world.

I may give another instance, which, from having passed under my own eyes
has much struck me. In a memoir on Fossil Sessile Cirripedes, I stated
that, from the large number of existing and extinct tertiary species;
from the extraordinary abundance of the individuals of many species
all over the world, from the Arctic regions to the equator, inhabiting
various zones of depths, from the upper tidal limits to fifty fathoms;
from the perfect manner in which specimens are preserved in the oldest
tertiary beds; from the ease with which even a fragment of a valve
can be recognised; from all these circumstances, I inferred that, had
sessile cirripedes existed during the secondary periods, they would
certainly have been preserved and discovered; and as not one species had
then been discovered in beds of this age, I concluded that this great
group had been suddenly developed at the commencement of the tertiary
series. This was a sore trouble to me, adding, as I then thought, one
more instance of the abrupt appearance of a great group of species. But